Device for predicting values of a fluctuating system at a predetermined future time



May 26, 1959 w. H. NEWELL E-rAL- 2,888,203

.DEVICE FOR PREDICTING VALUES OF A FLUCTUATING SYSTEM AT A PREDETERMINED FUTURE TIME Original Filed May 29, 1953 4 Sheets-Sheet `1 N I I v fP- Vfff; WL v e aff/f5 p /V VE /V 7019.5

' W. H. NEWELL EVAL May 26, 1959 v 4 2,888,203 DEVICE FOR PREDICTING VALUES oF A FLUCTUATING SYSTEM AT A' PREDETERMINED FUTURE TIME Original FiledMay 29, 1953 4 Sheets-Sheet 2 FLSp - a SEBI/G EWELL ET AL 2,888,203 DEVICE FOR PREDICTING vALUEs oF A ELUCTUATING May 26, 1959 w. H.

' SYSTEM AT A PREUETERMINED FUTURE TIME .4 Sheets-Sheet 3 Original Filed May 29, 1955 /maf of Ramen/,ye 200 @QN BUFFER HNPL/F/ER 22 A Trag/VEY DEVICE FOR PREDICTING VALUES F A FLUC- TUATING SYSTEM AT A PREDETERMINED FUTURE TIME William H. Newell, Mount Vernon, Edward G. Burgess, Jr., Kew Gardens, Norman J. Zabb, Brooklyn, and Stamates I. Frangoulis, Flushing, N.Y., assignors to Sperry Rand Corporation, a corporation of Delaware Original application May 29, 1953, Serial No. 358,324. Divided and this application February 28, 1955, Serial No. 490,763

7 Claims. (Cl. 23S-180) The present application is a division of application Serial No. 358,324 filed May 29, 1953.

The present invention relates to a method and apparatus for computing the characteristics of a fluctuating system continuously for successive future periods, and although it has a wide range of utility, it is particularly useful in predicting the future pitch angle (deck tilt) and the future heave (level) at a future time of a floating platform, such as the ight deck of a carrier.

In guiding an airplane in its approach towards a floating platform, such as the deck of a carrier for landing, it is necessary to predict the time of landing and the pitch angle and heave of the deck at the predicted time, to assure safe landing. Since the carrier is continuously oscillating in pitch and has a continuous oscillating vertical movement during the approach of the airplane, it becomes necessary to compute continuously the characteristics of the fluctuating motions of the carrier and to predict therefrom the pitch and heave of the carrier at the future predicted time of landing. Since the movement of the deck does not follow a uniform mathematical pattern or equation, it is seen that the matter of determining with accuracy the pitch and heave at a future time is not a simple problem.

One object of the present invention is to provide a novel method and device by which the characteristics of a fluctuating system may be computed and predicted continuously for successive future periods, even though the form of the system may be continuously varying and the variations in the system may not be following continuously any predetermined mathematical pattern or equation.

Another object is to provide a novel method and device by which the future pitch angle of a floating platform, such as the ight deck of a carrier, at the expected future instant of landing can be computed and predicted.

A further object is to provide a novel method and device by which the future heave or ight deck level of a oating platform, such as that of a carrier, at the expected future instant of landing can be computed and predicted.

In accordance with the present invention, the value of a fluctuating system at a future predetermined time is determined by continuously determining a number of past values of said system spaced at predetermined intervals, and starting continuously from the present and from said past values determining the value of said system at said future time.

In its more specific aspects, the invention is employed for continuously predicting the pitch angle andl heave.

nited States Patent of a iioating platform at a future predetermined time, by determining a number of past values of pitch angles and of level spaced at predetermined intervals, and from said past values determining the pitch angle and level at said future time. The operation is continuous in that the future characteristics of the pitch angle and level iuctuations are calculated on the basis of past performances, and as the past values change and deviate from the calculated characteristics of the system, the future calculated characteristics are correspondingly changed.

Various other objects, features and advantages of the present invention are apparent from the following description and from the accompanying drawings, in which- Figs. 1 and 2 conjointly show diagrammatically a pitch prediction computor embodying the present invention and employing past values of pitch angle as inputs, the solid lines indicating mechanical movements and the dotted lines indicating electrical signals;

Fig. 3 is a diagrammatic view of a follow-up unit employed to convert the signal voltages representing past values of pitch angle into shaft rotations proportional to these voltages, for use as inputs into the mechanism of Figs. 1 and 2, the electrical signals being indicated in dotted lines and the mechanical movements in full lines;

Fig. 4 is a diagram of the pitch angle curve recorded in accordance with the operation of a stable element and employed for obtaining past values of pitch angles and shows in conjunction therewith the output voltage for one pitch angle value obtained by a pitch pick-oli and signal modifier shown in Figs. 5 and 6.

Fig. 5 shows diagrammatically the television pick-off device employed in conjunction with the pitch pick-o5 and signal modier of Fig. 6;

Fig. 6 shows diagrammatically the pitch pick-off and signal modifier for obtaining past values of pitch angles in the form of electric signals, the full lines representing electric signals, the dotted lines mechanical movement such as shaft rotation; and

Fig. 7 is a diagram of the trigger circuit and the gated sweep cut-off employed as part of the system of Fig. 6.

To predict the position of a -ships deck at the future instant of landing of an approaching plane, it is required that the time ahead when the plane is expected to land be predicted and then that the position of the deck at this time be predicted. This sequence of predictions is based on the assumption that the pilot has sole control of the plane speed and that the position of the deck at touchdown (the position on the deck where the plane can begin to land) is not preselected.

The time required by a plane to fly from its present position to its position at touchdown on the deck indiu cated herein by the symbol Tp can be calculated in the manner described in the aforesaid copending application. For computing the predicted pitch angle of the deck at the predicted time Tp of landing indicated by the symbol Pp and the predicted deck height at the predicted time Tp indicated by the symbol Hp, it is necessary to determine continuously the present pitch angle of the deck indicated by the symbol Po and the present deck height indicated by the symbol H0.

To supply continuously information on the magnitude of the present shippitch angle, service of a stable elel ment is required. This stable element could be of any well known construction. For example, it could be one of the stable elements commonly employed in connection with ring control systems in warships, except that it would be provided with means for transmitting the pitch Po to a recorder from which the past values of the pitch angle at previously spaced intervals may be determined; as will be more fully described. There is also the possibility that the stabilizer unit required in connection with the radar antenna drive could also be used to supply continuously the information Po and from that information the past values of the pitch angles required could be obtained.

Continuous measurement and supply of the information Ho, i.e. the vertical motion of the ship, can be obtained'and recorded from an accelerometer ofthe type shown and described in the aforesaid copending applica-I tion, andfromthat information, they past values of the deck level could be obtained.

Having determined a value for the prediction timel Tp,"the s'econd'p'hase of the prediction problem is en:`

tered into, namely the'deck tilt Pp atthe: future timeTp. Consider first a Vship at rest in Stillwater. If now a moment*k should be applied about an athwartship, axis through the center of'gravity, some pitch angle, 'sayy P would result. Upon removal of this applied moment, the ship would oscillate in pitch about the athwartship axis with decreasing amplitude, the equation of motion being approximately 113+ci +1 1 =o (1s) where I is the effective longitudinal moment of inertia of the ship about the athwartship pitch axis, C is the damping moment coeicient due to skin friction and the like, K is the hydraulic restoring moment coeicient, P is the second derivative of the pitch angle, with respect to time and P is the first derivative of the pitch angle with respect to time. Now the period of this oscillation is the pitching period of the ship and is equal to where Wnp=natural angularfrequency of pitch. However, when the ship is in a seaway, the equation of motionr(18) becomes where F (t) represents the pitchrcomponentlof the moment applied to. theship by waveaction. Now from generall observation, it can bersaid that FU), although highly variable, will nevertheless at a given hour exhibit a frequency spectrum in which certain narrow bands of frequencies are predominant. From an analyzed rec- Ording of pitch angle of various type ships headed into the`wind under different sea conditions over extendedl rolling andlh'eavingicause an induced pitch. c Usually, but 1 not always, therewill be asingle systemiof waves run-N.

ning. Furthermore, thisY system of waves will more often than not be running in nearly the same direction as the wind. Hence, the normal expectation during carrier landing operations is that the ship would be headed 1n a direction about opposite to that in which the waves are traveling. Considering that the usual period of ocean waves is in the range of 5 to l0 seconds, a ship speed of 25 knots would reduce these periods to the Arange of From thisV 1.8 to 5.5 seconds. It almost seems from these considerations that under such conditions, the only period to be seriously considered in pitch motion would be the natural pitch period. That is, a forcing moment function of 2 second period would have to be of tremendous magnitude to appreciably affect the ship motion in pitch. However, a forcing function of 5 second period might well have an appreciable effect, and of course a longer period forcing function would have still greater influence. Functions having such longer periods would arise if the normal conditions outlined above did not hold-as for example, when the wind is opposite in direction to the sea and the ship is traveling with a following sea.

From the above discussion, it is evident that an exact solution for the equation of motion of the ship is not possible- However, the equation of motion. may be represented with Sufficient accuracy byl the.r approximation where FU) is. a, Sine.- function of unknownA amplitude e.. angular frequency w and, phase angle a. The solution of this differential equation is then of the, form w1 and wz being the unknown angular velocities and 4:1 and 412 the phase angles of the simple harmonic motions of which the pitch angle is assumed to be composed. This form, involving the six unknown parameters a1, a2, w1, W2, p1 and 2 therefore. represents the time variations of pitch angle. Hence, if these six unknowns and variable parameters can be continuously determined and furthermore if a continuous value of prediction timeTp is available, then the predicted pitch angle is The problem is now therefore reduced to the continuous determination of the six unknown and variable parameters noted above.

In the form of mechanism which can be employed in accordance with the present invention to determine the predicted pitch angle Pp, it is assumed in Equation 2O that a1=a and 112:0, so that P=a4 sin (wt-hip) (22) Considered here as known-quantities are the present valuel of pitch angle P as well as the ratesv of change P, etc.

Furthermore, if means are provided for recording P, the

valuesof -P and its'rates at any past instant of'timeawill be known. From this known data, thevquantities a, w and qb which are for the present-considered to be constants, must be determined.l Now this evalutionmay beY carried out in accordance-with the present invention, as

P gewaden geef-Kwaad.,

ietc.

thereby obtaining a' series of third order determinants equated to zero. For example, the iirst vof these is 13mr e-lwf eher :o

P Br e-Zwr 82h" Now let x=e, so that the above determinant becomes P-, :c-l a: =0

P-zf z" P.r a: :c =0

P-2, 1 'x2 Operating on this form, we obtain after successive reductions P-l-P-zf, :vz-l-l Pq, :a That is (P+P 2,)x-P (x+1)=0 Similarly (30) will be the relation derived from the set composed of the second, third and fourth equations in the set (29). The fact that the pair of Equations 30 must be consistent, requires that for a pure sine variation, the measured values of pitch angles at the equal spaced time intervals t-3r, t-21, t-r and t satisfy the relation P +P-zn P-f =0 (31) P-r'i-P-n P-Zr Suppose now that we make the time interval 'r equal to the prediction time TIJ and write P 7p=P Then we may obtain the following relation similar to Equation 3l Thus, if we know from a recording of pitch angle, the magnitude of this angle at the present time and at the past time intervals -Tp, -2Tp, then we can determine the magnitude of the pitch angle at the future time TD from the Relation 32, which is a linear equation in Pp of the form The above analysis may be extended to handle a pitch angle variation of the form of Equation 20, which is To carry this out, the rst series of equations is written From the first five of the equations in the set (33), We can eliminate the four quantities The result of this elimination written in determinant form is Pp ewiT, e-t'wiTp ewg T, e -wzTp P p e umn eiwlT, e-twiT, eiwsT :0

P zp e 21mm ezzwl Tp e ziwi T, e 2m: Tp

Pap e am T, e siwi Tp e 3fm T, e Siwa T Now let ewm1=x and ewm=y, then the determinant (34) may be written P w V1 y irl P x-l :c y-l y =0 P-zp V2 m2 y-Z y2 P ap 3;-3 xs y-a ya and this is equivalent to P :1:3 :n y' y P D x2 x2 ya y2 :0

P-zp x w3 y .113

P gz, 1 :i:4 1 g4 35) We may in like manner obtain four other determinants similar in form to (35) of which the irst one is 13-4 1 x4 1 g4 v Now these ve determinants are such that the minors 7 of corresponding'elements in the rst'column Vof 'each are equal, so that we have in eiect ve linear equations in ve unknowns, namely, the first minors of the elementsin the first column. The condition that these tive equations be consistent,l gives then the relation this is equivalent to P, :a4-1 0 y4-1 1 P :v3-I rv-y 243-1/ y P-, rc2-y2 0 y2=0 P-zp w-ra 20a-ys y-z ya P 3 1--azz4 hr1-g4 1-y4 g4 By a sequence of reductions, this becomes Where X and Y are functions `of the unknown angular velocities "w1 and'wz of the harmonic motions of which the pitchangle is rassumed't'o ybe composed. The general method of solution adopted is rst to determine X and Y from the second and third Equations and 4l. These values may `next be substitutedzin the rst Equation 39 which can then be solved for the desired quantity Pp. Since it is desired to solve .Equations 40 and 41 bymmeans @freed-back, .as will bedesci'ibed, We must determine the necessary conditionsrfor this processto be stable. This is equivalent arithmetically speaking, to determining an iteration process for approximating X and Y which is convergent to their true values. Suppose initially that Equations '40 and 41 are not satisfied, so that we may write them of change of p. is never positive and not equal to zero unless e2 and e3 are zero, then since u is always positive 35 from (44), the limit of ,u as timeV increases must be zero This relation in turn is equivalent to the linear equation Since the set of Equations 37 must befconsistent, it follows that This relation can be mechanized for the determination of the pitch prediction Pp, in the manner to be described.

The quantity P in the Relation 38 is the quantity Po, the present pitch angle, which is available as a shaft rotation from the vstable element, as already described. The quantities P p, P zp P 5p giving past values of pitch angle at the respective times -Tp, 2Tp -5Tp, or represented as -p, -2p etc., are available as voltages proportional to them by a mechanism to be described and shown in Figures 4, 5 and 6. The Relation 38 'with the substituted notations indicated is and hence the limits 'of @Zand e3 must-'also'be'zerm :We have for the time rate of change of-,u the expression These expressions for the partial derivatives are substituted in Equations 46, resulting in and and

It is apparent that in the mechanism, 'an appropriate linear combination of the error signals e2 and e3 must be formed before feeding these quantities back into the mechanism to adjust the magnitudes of X and Y in such a manner that they converge to the correct values, obtained when e2 and e3 are both zero.

In the above analysis, it was assumed that the various coeicients, such as P-|-P 2p were constant. Actually, these quantities Will go thru a cycle of sinusoidal variation in about ten seconds. Hence, the quantity any of the coeicients. It can be shown that Equation 47 may be replaced by the inequality du i C# Where C is a positive constant or Q di Integration of Equation 50 gives in Which has the absolute value.

Here, the constant C may be made as large as desired by increasing the sensitivity constants k1 and k2. As a result, the `settling 4time can be made short enough so that X and Y follow their values corresponding to the changing set of coefficients.

Special conditions would arise when w1=w2. In such a case, Equations 40 and 41 are not independent and their formal solution would give indeterminate values for X and Y. However, ythe mechanism to be described, as constructed will still give some pair of values for X and Y which satisfy Equations 40 and 4l and there will be a singly inlinite set of such solution pairs. Hence, we shall have for any value of X If now this value of Y is substituted in Equation 39, the result is equivalent to Accordingly (52) in accordance with Relation 51. The solution given byv Equation 52 is satisfactory if P Z,+P Bp0.

Therefore, there is obtained for w1=w2, the correct.. value of Pp independently or the particular value of X,. so long as XeO and P P-I-ILSO. We have now two] conditions to consider. In the first condition, we may have X =0 instantaneously due to the temporary vanish ing of the determinant P-v'l'P-Bv P -211 when w1w2. This event will not disturb the continuit)r of the solution for Pp. In the second condition, however, X might conceivably remain on Zero for an ap preciable time. This is possible only when w1=w2 and: X is indeterminate. Thus We make provision here by` means of a time delay relay operating when X=0 for time r to ensure that X has an arbitrary non-zero value.. A similar situation exists in regard to the quantity (P p{-P 3p). Thus P -f-P 3p will remain on zero for an appreciable time only if w1=w2=0. If P p-i-P 3p=0' for an appreciable time, it indicates that there is no pitch motion and hence P=PO, in which case a time delay relay is employed to take care of this situation. The mechanism 144 for solving equations equivalent to Equations 39, 40 and 4l is illustrated in f Figures 1, 2 and 3. In this illustration, the mechanical movements such as shaft rotations, are indicated in full lines and the electrical signals such as voltage signals are indicated in dotted lines.

The pitch prediction computer 144 illustrated in Fgures l and 2 requires as inputs besides the present pitch angle P0, the past pitch angles P p, Pnzp, P '3p, P 4p and P 5p as shaft rotations. These past pitch values P kp are obtained as voltage signals as shown in Figures 4, 5 and 6, in a manner to be described, and are then converted into shaft rotations proportional to these voltages by a servo follow-up control unit 145 shown in Figure 3, for introduction into the pitch prediction computer of Figures l and 2. This follow-up unit 145 is similar to the follow-up unit employed in the heave meter shown in the aforesaid copending application, for converting the assegna 11 tier 147 for the output signal fromfthef. adding network. A potentiometer 148 supplies the matching voltage and a generator 150 supplies anticipation to prevent oscillation of a servo motor 151 while following a variable signal.

Having now obtained all the necessary quantities P kp, and having available Po as the shaft rotational output of the stable element, we add these quantities by the mechanical differentials 155, 156, 157, 158 and 160 (Figures 1 and 2) to obtain the coefficients respectively, in Equations 39a, 40a and 41a;

The next step is to obtain voltages proportional to the terms in the three Equations 39a, 40a and 41a. For example, the term (Po-l-P 4p)X for Equation 40a is required as voltage. As indicated in Figure 1, this voltage is the output of a potentiometer 161 whose inputs are X, constituting the feedback voltage on the winding, and P1-P 4p, the mechanical setting of the potentiometer slider, derived from the mechanical differential 156. Similarly, the term (Ppl-P 3p)Y for Equation 40a is obtained as the output of a potentiometer 162, whose inputs are the feedback voltage Y and the value P p-{-P 3p derived from the mechanical differential 157. The three voltages (P0-{-P 4p)X, (Pp-l-P 3p)Y and P ,gp (original signal Without conversion into shaft rotation) are now added in a network 163 to obtain as output the error signal e2 which is zero when the Equation 40a is satisfied.

In a similar manner, through the potentiometers 164 and .165, we obtain voltage signals (P p-l-P 5p)X and (P 2p{-P 4p) Y, and these are combined in the network 166 with the original signal P 3p (without conversion into shaft rotation) to obtain as output the error signal e3, which is zero when the Equation 41a is satisfied.

In the method of solution here adopted, the error signals e2 and e3 must be combined in denite linear combination for each feedback, in order to secure stability of operation, as previously shown. These linear combinations are given in Equations 48 and 49. Thus the voltage e2 isl applied to the winding of a potentiometer 168, whose slider input is POA-P4P, a power driven rotation, to obtain the output voltage 2(Pp-}P 4p)ez. Likewise, the voltage 2(P p-l-P 5p)e3 is obtained as the output of a potentiometer 169. These two voltages are added in the adding network 170 to obtain the output =X=-2k1[ P.+P f2+tP-.,+P 5, e3i

in accordance with the theory of stability previously de'- veloped and indicated by Equation 48.

Similarly, through a potentiometer 171, an output is obtained therefrom having the magnitude 2 PZpiP-4p)53 and through a potentiometer 172, an output is obtained therefrom having the magnitude 2(P p-l-P 3p)e2. These two-voltages are added in the adding network 173 in accordance'with Equation 49 to obtain dY', rt==Y=r 2k2[(P-v+P-ap) 52+ (P-2v"i"P-4v) @si The voltages X 'and Y are then fed to the integrating networksJ1'74 and 175 respectively to obtain output voltage X1 proportional to voltage X from one network and voltage Yi proportional to voltage Y from the other network; As long as .Xi-7&0, Xi=X.

Having the voltages X'and Y, we now dealwith Equationvfgay toobtain the desired pitch prediction Pp. For

that purpose, we add the quantities P 3p and Pp (outf and the quantity P p employed in its original voltage form Without conversion into shaft rotation, are added in a network to obtain the error signal e1 in accordance with Equation 39a. To obtain stability of feed back foi" this single Equation 39a, we must have according tothe original analysis equivalent to Equation- 39a.

.=--'21Lt Xadt (54a Hence, by multiplying the error signal e1 by the quantity X and integrating the product, there is obtained the feedback Pp. The settling time can be made suciently small by increasing the sensitivity factor k.

To obtain the quantity Pp in the final stages of the cornputer inaccordance with the Equation 54, the voltage X is converted into a corresponding shaft rotation by a follow-up unit 181, similar to that illustrated in Figure 3, and this shaft rotation and the error voltage signal e1 are supplied to a potentiometer 182 to obtain the quantity Pp which after integration in the network 183 results in the value Pp as a voltage. This voltage Pp is converted into corresponding shaft rotation before being sent out of the computer, by a follow-up unit 184 similar to the follow-up unit of Figure 3.

As already indicated, there are two conditions that must be provided for to assure continuous operation of the computer. Those conditions are when X=0 for an appreciable time 1- and when P p-l-P 3p=0 for a time 1- which may amount to about 0.1 of a second. For that purpose, there is provided a time delay relay unit 185 having one mechanical element operated by the mechanical quantity P p-l-P 3p and having a lead from a voltage reference source connecting through a switch in said unit into a linev connecting into a relay unit 186 located between the integrating network 183 and the follow-up unit 184. When the quantity P p-|-P 3p equals zero, indicating there is no pitch motion and that therefore Pp=Pa, this condition imposed on the time delay relay unit 185, will cause a switch to close in said unit, so that the reference voltage actuates a relay in the unit 186 and closes thereby a `circuit from a signal line carrying a voltage signal P0 tothe outlet ofV said unit and in turn to the output of the computer, while the connection in said unit-186 from the outlet of the integrating network 183 to the inlet of the follow-up unit 184 is opened. As soon as normal conditions are restored in which P p-{-P 3p70, the switch in the unit 185 establishing a circuit between the voltage reference line and the unit 186 is opened, so that the Pp signal from the output of the integrating network 183 has a through circuitthrough said unit 186 to the follow-up unit 184, while the circuit of the voltage signal assegna To provide for the condition when X =0, for the time r, there is provided a time delay relay unit 190 between the integrating network 174 and the potentiometer 177. When Xi=0, a relay in the unit 190 closes a switch therein to establish connection between a voltage reference signal line and the output of said unit, while the circuit between the output of the integrating network 174 and the output of said unit is opened. At that instant, X =V ref. When Xi is no longer equal to zero, the circuit between the voltage reference signal line and the output of the relay unit 190 is opened, while the through circuit between the output of the integrating network 174 and the output of the relay unit 190 is reestablished.

In the pitch prediction computer of Figures 1 and 2, the past values of pitch angle at the respective times -Tp, --2Tp --5Tp were employed as inputs, some in the form of voltages and others in the form of shaft rotations. Before such quantities are obtained, a recording of the pitch angle Po in the form of a black single line curve on a white background is made. This recording is made from the output of the stable element in any suitable manner, as for example in the manner shown in Figure 4. For example, the stable element is made to rotate a screw 200 in accordance with the variation in pitch angle with time. This screw 200 has threaded thereon a sleeve 201 carrying a pen 202 registering on a roll 203 moving lengthwise at a predetermined constant rate to produce an undulating record 204 which is a measure of the pitch angle of the carrier deck. In accordance with one method of the present invention, the quantities P p, P gp P 5p representing the amplitudes of the record 204 are picked off at corresponding times -Tp, -2Tp, etc. and translated into voltages. For that purpose, the past record 204 is continuously focused as shown in Figure 5 on the screen 205 of a television pickup camera 206. This past record should cover the range from t= to t=5Tp where Tp has some maximum Value, say 30 seconds, as shown in Figure 4. Accordingly, the horizontal displacement of the camera scanning beam will represent time while the vertical displacement will represent amplitude or the magnitude of P t. Therefore, the scanning beam deflection coil circuit is arranged to obtain a single vertical sweep at horizontal deflections corresponding to the times Tp, -2Tp, -3Tp, -4Tp and STP in succession. If now, a charging circuit is triggered at the start of the vertical sweep and is opened by means of the pulse occurring when the vertical sweep beam crosses the curve image, there is obtained a voltage which, when diminished by a reference voltage, will be proportional to the amplitude of pitch at the time required. This arrangement is illustrated in Figure 4 for the vertical sweep at t=-2Tp.

The complete scanning cycle, consisting of the five vertical sweeps might be carried out hundreds of times per second, `so that the five output voltages representing P kp would after appropriate smoothing be quite continuous and suitable for transformation to mechanical rotations for use in connection with the pitch prediction computer of Figures 1 and 2. The devices necessary to carry out the operations indicated are shown in Figures 5, 6 and 7. In Figure 6, the solid lines represent electric signals and the dotted lines mechanical displacements, and specifically shaft rotations.

Referring specifically to Figure 6, the pitch pickoff and signal modifier system 209 shown comprises a crystal or oscillator 210 of well-known type, which is the primary source for the timing of all the operations and steps of the system. The oscillating rate of the crystal oscillator 210 is not important from the point of vieW of actual time measurements, since a submultiple of rate is employed in the system to control the sequences of operation at predetermined time intervals. The frequency of oscillation of the crystal oscillator 210 may be in the neighborhood of 100 kilocycles and this may be reduced to possible kc. by frequency division, to give for example 1000 complete cycles of operation of the system per second.

The output of the crystal oscillator 210 is a sinusoidal voltage of predetermined frequency, as for example 5 kc. frequency. This voltage is applied to the control grid of a multi-grid high-gain tube in an amplifier clipper 211 of standard construction to amplify the signal from the crystal oscillator and at the same time clip off the crests of the sine wave voltages to produce a square Wave voltage more suitable for the timing and synchronizing of the different operations of the system.

The output from the amplifier clipper 211 is imposed upon a sampler gate generator 212 which has connections to five circuits, each adapted to produce an electrical signal corresponding to one of the past values of pitch angle desired. This sampler gate generator 212 is essentially a combination of five multi-vibrators, one for each circuit and supplies during each complete cycle of operation, five pulses in succession, one to each of the separate circuits. Each of these impulses serves to close a connection (by rendering a tube conductive) through la gated amplifier 213 and a gated sweep cut-off 214, in

one of the five circuits corresponding to the phase of the impulse. The sampler gate generator 212 and the five gated generators 213 serve thereby essentially as an electronic commutator.

Each of the gated amplifiers 213 is of standard well known construction and consists essentially of a tube with two grids, the screen grid being connected to the sampler gate generator 212, the control grid being conf nected to a voltage proportional to -nTp. The gated amplifiers 213 are normally non-conducting. When an impulse is received by a gated amplifier 213 from the sampler gate generator 212, said gated amplifier becomes conducting and an impulse is sent thereby proportional in voltage to -nTp to a pick-off iconoscope 215 (Figures 6 and 7). This positions an electron beam 216 in said iconoscope in the horizontal or time direction. The beam is then in position to scan vertically across the image of the curve 204 (Figures 4 and 5) projected upon the iconoscope mosaic 205.

Each gated amplifier 213 has two inputs, one from the sampler gate generator 212, as described and the other from a voltage divider 218 comprising a series of resistances 220, arranged to divide an incoming voltage which is vproportional to 5Tp and to allocate to each of the five gated amplifiers 213 a voltage proportional to the value of -nTp selected for the circuit of that amplifier. The input voltage into the system is obtained from a shaft rotation (dotted lines) representing Tp obtained from the prediction time computer shown and disclosed in said copending application. This shaft rotation is made the input of a linear potentiometer 221 (Figure 7) having a certain constant reference voltage applied to its total resistance. The output voltage of the potentiometer is therefore proportional to -5T1 and this voltage is applied to the terminal of the voltage divider 218 having the five fixed resistances 220 between taps. In this manner, voltages proportional to -5Tp, -4Tp, -3Tp, 2Tp and -Tp are obtained as inputs to the control grids of the gated amplifiers 213.

When a gated amplifier 213 becomes co-nducting as the result of an .im-pulse received from the sampler gate generator 212, as already described, the voltage passing through said gated amplifier proportional to --nTp is impressed upon the pick-oft` iconoscope 215, and this detiects its electron beam 216 horizontally to the abscissa value corresponding to the -nTp value of the image to be scanned. The extent of horizontal deflection of the electron scanning beam 216 is dependent upon the Voltages impressed and is controlled from the crystal oscillator 210 through the amplifier clipper 211, as will be described, and since these voltages are proportional to the values n'l`p, the location of the `scanning beam in its proper horizontal position is assured.

As soonasthe electron scanningbeam 216 from the iconoscope 215' has been properly located horizontally,`

an impulse'is sent from the oscillator controlled amplifier clipper 211 to a vertical sweep generator 223, and this initiates the vertical sweep of the electron beam 213 along the selected -nTp abscissa value.

The vertical sweep generator 223 is of standard well known construction and includes a charging condenser. As the electron beam 216 moves vertically the condenser is charged at a voltage which ordinarily is exponential in character but which is linearized by means of a bootstrap circuit, so that the characteristics of this voltage during the vertical sweep are as indicated in Figure 4. As the electron beam 216-in its vertical sweep crosses the image being scanned, an impulse or pip is sent from the iconoscope 215'to a ybuffer amplilier 224 of well-known construction, to amplify the impulse and also to isolate the iconoscope 215 yfrom a trigger circuit 226.

The electron lbeam 216 continues its vertical sweep beyond the crossing point of the image being scanned to a predetermined point and then returns vertically ybut more quickly towards its original position for the next horizontal sweep sequence. During this return trace, the electron beam 216 recrosses the image being scanned,

and may send another impulse from the iconoscope 215 towards the butter-amplifier 224. To prevent this condition, a blanking gate generator 227 is provided controlled from the oscillator 210 through the amplifier clipper 211 and'serving to impose a blankingvoltage to the-'bulfer amplifier 224 during vertical return trace or fly-back time.

The trigger circuit 226 serves to freeze or clamp the voltage developed during charging in the vertical sweep `generator 223V to the value it had when the electron beam 216 crossed the image `being scanned. This voltage while it is building up in the vertical sweep generator 223 during the vertical sweep of the electron beam 216 is amplitied in a Asweep amplifier 228 and then impressed upon one of the gated sweep cut-oifs 214 in the -rzTp circuit.

Each gated sweep cut-off 214 (Figures 6 and 7) comprises a gated amplifier 239 connected to a diode circuit 231 and having its screen grid connected to a bistable trigger circuit 232 incorporated as part of said cut-olf, and its control grid connected to the output of the sweep amplifier 228. One of the triode tubes 233 of the trigger circuit 232 has its grid connected to the output of the sampler gate generator 212 and isV conductive in stable condition of the trigger circuit, while the other triode tube 234 of said trigger circuit has its grid connected to the output of the trigger circuit 226 and is non-conductive in stable condition of the trigger circuit 232.` As soon as a gated amplifier 213 is rendered conductive by an impulse from a corresponding multi-vibrator unit in the sampler gate generator 212, this impulse is sent at the same time to the corresponding gated sweep cut-oft 214 and through the conducting triode tube 233 in the trigger circuit 232 of said cut-off, as a positive impulse upon the screen grid of the gated amplifier 231i. When the voltage is impressed upon the control grid of a gated amplifier 231i by an impulse from the sweep amplifier 228 generated when the electron scanning beam 216 starts its vertical scanning sweep, the gated amplifier 23() in the cut-off 214 becomes conductive, so that a linearly increasing voltage is conducted through said gated amplifier and through the diode circuit 231. tron scanning beam 216 during its vertical sweep crosses the image, the resulting impulse from the bufferV amplifier 224 impressed upon the trigger circuit 226 causes said circuit to send out a negative impulse to the grid of the triode tube 234i in the trigger circuit 232 of the gated sweep cut-off 21C-, and causes thereby the tube 233 of lsaid trigger circuit 232 to become non-conductive and the other tube 234 to become conductive. The resulting negative impulse impressed upon the screen grid of the gated amplifier 23) of thecut-off 214 renderssaidampli- When the elecl er non-conductive, so that the charging voltage in the diode circuit 231 which has been increasing is clamped at the value it had upon the image crossing. The diiference between thisI clamped voltage and a reference voltage is available at the outlet of the diode circuit 231 and this output value which is proportional to P ni, as indicated in Figure 4 is smoothed by a network 236 of the type disclosed in the aforesaid copending application, so that a continuous value of P rlp is obtained.

The trigger circuit 226 shown in Figure 7 is monostable and comprises a triode 240 and a triode 241 having a common cathode resistor 242, so that when triode 240 is conducting, triode 241 is cut off. During normal conditions, the trigger circuit 226 is in stable condition, i.e. the tube 240 is conducting and the tube 241 is not conducting, and no impulse is being sent from the trigger circuit 226 to the gated sweep cut-off 214i. When a negative impulse is received from the buifer ampliiier 224 as a result of the electron beam 216 crossing thev image being scanned, it is amplified Vby the tube 240 and applied as a positive impulse to the grid of the tu'be 241. This causes the voltage on grid of the tube 240 to assume negative value, cutting-off tube 240 while tube 241 starts conducting. The output of the trigger circuit 226 to the gated sweep cut-off 214 also assumes a negative value and this serves to freeze or clamp the charging voltage to the value dependent upon the curve image cross-over point of the electron beam 216 as described.

Although the tive P np circuits are activated successively through the sequential impulses sent out from the sampler gate generator 212 successively to said circuits, the voltage quantities P 5p, P4P, P gp, P Zp, and P p are continuously and simultaneously obtained and these are made available to the pitch prediction computer shown in Figures l and 3, after being converted into corresponding shaft rotations by follow-up units such as shown in Figure 3.

The present pitch angle P0 which is obtained as a shaft rotation from the output of the stable element is made available as a voltage signal for use in connection with the switch 136 in the pitch prediction computer of Figure l, by applying the present pitch angle P0 as a slider displacement to potentiometer 245 (Figure 6) and at the same time applying a referenence voltage to said potentiometer. The output of this potentiometer 245 will be an electric signal,

It is possible to modify the Relation 38, so that it isk not necessary to take observations of P so far back in the past. For example, we may write and using the 'formula for the sum of the sinesv of two angles Similarly In these Equations k, q, m and n are constant multipliers for the prediction time intervals The two quantities 2111 sin [w1(t{-kTp)-l1] and (59) Two relations similar to 59 can be obtained by replacing k by k and k". v

Thus a generalization of the Equation 38 is obtained by eliminating the expressions involving w1 and W2 from the Relation 59 and the two similar relations. The result is nally ,deck height Hp is made from the output of the heavemeter (accelerator) shown and described in the aforesaid copending application. From the resulting record pro.- duced in a manner similar to that shown in Figure 4, the quantities H p, H 2p P 5p representing the amplitudes of this record are picked oit at corresponding Relation 38 is the special case of 60 with k= -'1 C',=2 kil: 3

It is apparent that we must have k k' k 0 since if k=0, then Pq or P q and Pm or P m are both unknown future values of P Whereas only one `future value of P is desired and can be determined from the Relation 46() alone. We also have the simple relations If, for example, k=1/2 then q=i72, m=1/2, k'=-%. In addition, we might take n=0, k"=.-2 and let Tp be represented by p, so that the Relation 60 becomes P-izJI-P-Zm P-zflP-s/m 2P2r (61) It should be noted that observations are required at the past intervals given by -1/2Tp, -Tp, -%Tp, -2Tp, -/2Tp, -3Tp and -7/2Tp as well as the present, making eight observations in all. This number is two more than the minimum number of observations required as dicated by the 6 parameters involved. Using the Relation 6l, the time interval required for past sampling is reduced from -5Tp to -72Tp or by 30 percent.

Another such relation requiring nine observations is and here the reduction in time interval is 45 percent.

The means for obtaining the values of pitch angle in the past at the special intervals indicated is similar to that shown in Figures 4-7, and the mechanism for predicting the pitch angle Pp from these past quantities would be similar to that shown in Figures 13 and 14.

Equations 39a, 40a and 41a may be mechanized by the mechanisms of Figures 1-7, to determine the value of Hp (predicted deck height at predicted time Tp of landing) exactly as was the value Pp (predicted pitch angle of the carrier at the predicted time Tp). In that case Equations 39a, 40a and 41a become times -Tp, -2Tp, etc. and translated into corresponding voltages by mechanisms similar to those shown in Figures 5-7. These voltage quantities H p, H 2p P 5p converted into corresponding shaft rotations by a servo followup control unit similar to that shown in Figure 3 are fed into the mechanism similar to that shown in Figures l and 2, to mechanize Equations 3917, 4Gb and 4lb for the value of the quantity Hp.

The mechanisms shown and described may be set up as part of a system for guiding an airplane in its approach towards the flight deck of a carrier, as shown and described in Vthe aforesaid copending application. However, as far as certain aspects of the invention are concerned, the method and mechanism of the present invention may be employed for continuously predicting the future value of a quantity in a uctuating system, by continuously determining the past values of the quantity at spaced predetermined time intervals, and employing these past values as inputs to determine the future characteristics of a uetuating system from which the value of the quantity at a predetermined future time is computed.

In the following claims the symbols Tp, P, P p, P gp, P 3p, P 4p, P 5p and Pp have the general meanings indicated With application generally to liuctuating systems, unless specifically defined.

What is claimed is:

l. A device for determining the value Pp of a quantity in a fluctuating system at a future predetermined time, which comprises means for receiving as input quantities a number of past values P p, P Zp, P 3p, P p and P 5p spaced at predetermined intervals, means for receiving as another input quantity the present value Pp of said system and means for mechanizing with said input quantities the equations in which X and Y are functions of the unkown angular velocities of the simple harmonic motions of which the fluctuating system is assumed to be composed, to obtain the value Pp, the quantities X and Y being obtained by mechanizing two of said equations, and said quantities X and Y so obtained, being employed in mechanizing the other equation to obtain the quantity Pp.

2. A device for determining the value Pp of a quantity in a iluctuating system at a future predetermined time as described in claim l, comprising means for substituting in the mechanizing means for the determined quantity X a reference quantity when X :0, until conditions are restored in which X is no longer equal to zero.

3. A device for determining the value Pp of a quantity in a fluctuating system at a future time as described in claim l, comprising means for substituting in the mechanizing means for the determined quantity Pp the quan-t i@ tity Po, when the quantity P -l-P 3p=0, until conditions are restored in which the quantity P {P 3p is no longer equal to zero.

4. A device for determining the value Pp of a quantity in a flutuating system at a predetermined future time, which comprises means for receiving as input quantities a number of past values P p, P Zp, P ap, P 4p and P 5p spaced at predetermined intervals, means for receiving as another input quantity the present value Po of said system, means responsive to said input quantities for mechanizing the equations in which X and Y are functions of the unknown angular velocities of the simple harmonic motions of which the fluctuating system is assumed to be composed, and e2 and e3 are error signals, to obtain the values of s2 and e3, means for mechanizing with the determined values e2 to obtain the values of X and Y, means for mechanizing with the determined values X and Y the equation (Pp"iP-3p)Xi`(Po`iP-2p)Y-iP-pzfl-)O wherein e1 is an error signal, to obtain the value of said error signal e1, and means for mechanizing with the determined value of the error signal e1 and the value X the equation to obtain the value Pp.

5. A device for predicting the pitch angle of a floating deck at a predetermined future time as described in claim 4, wherein P p, P 2p, P ap, P .p and P 5p represent past pitch angles spaced at predetermined intervals, Po represents the present pitch angle and Pp represents the predicted pitch angle at a future time.

6. A device for predicting the height of a floating deck at a predetermined future time as described in claim 4 wherein Pw, P zp, P3p, P 4p and P 5p represent past deck heights spaced at predetermined intervals, Po represents the present deck height and Pp represents the predicted deck height at a future time.

7. A device for determining the value of Pp of a quantity in a fluctuating system at a future time, which comprises means for obtaining continuously in physical `form a number of past values of the quantity spaced at predetermined intervals from the present time, which intervals advance with said present time to maintain constant spaces of time between the advancing present time and the times of said past values respectively, and means responsive to the physical quantities representing said past values as continuous inputs for continuously mechanizing the equations References Cited in the file of this patent UNITED STATES PATENTS Roberts Dec. 23, 1952 Roberts et al May 11, 1954 OTHER REFERENCES Interim Report, Smith and Lowden, A Servo System Operating on Discontinuous Information, published in Great Britain, June 1950. NRL Document 57417. 

